New South Wales's prima facie limit, often signed by derestriction signs, was only enforced in cases where a driver's speed could be demonstrated to be excessive or dangerous in the context of prevailing road conditions. This was somewhat similar in principle to "reasonable and prudent" limits in other jurisdictions. This led to the widespread but misleading belief that no limit applied, and that derestriction signs indicated an "unlimited" limit. This belief, coupled with repeated studies showing 85th percentile speeds in excess of on major routes, comparatively high road tolls, difficulty in prosecuting speeding offences, and the variance in meaning of the derestriction sign across states, led New South Wales to harmonise its rural default limit to in 1978. The use of derestriction signs in New South Wales was officially discouraged, and on state controlled routes, signs were progressively used instead. See also Australian Road Rules References External links Metric Motoring (1973) – Original television advertisements explaining the conversion to metric speed limits. From the National Film and Sound Archive. Transport law in Australia Australia Road transport in Australia